Driver Assistance System for a Vehicle, in Particular Commercial Vehicle, and Method for Controlling a Brake System

ABSTRACT

The invention relates to a driver assistance system for a vehicle, in particular commercial vehicle, wherein the driver assistance system ( 14 ) has: a detection system which has at least one sensor ( 15 - 1, 15 - 2, 15 - 3 ) for issuing measuring signals (S 5 - 1 , S 5 - 2 , S 5 - 3 ), a control unit ( 16 ) for receiving the measuring signals (S 5 - 1 , S 5 - 2 , S 5 - 3 ) and for determining the probability of a critical situation or critical state of the vehicle ( 1 ), wherein, when a critical state or sufficient probability of a critical state is identified, the control unit ( 16 ) of the driver assistance system ( 14 ) outputs a signal (S 6 ) for priming a brake system ( 4 ) to a brake control device ( 6 ) of the brake system ( 4 ) of the vehicle ( 1 ), and wherein the control unit ( 16 ) outputs an external brake request signal (S 6 ) for initiating braking operations to the brake control device ( 6 ) of the brake system ( 4 ). According to the invention, in order to prime the brake system ( 4 ), the control unit ( 16 ) outputs an external brake request signal (S 6 ) which has a desired acceleration value signal (S 6 - 3 ) with a higher desired acceleration value (a-des) than a current actual acceleration value (a-act).

The invention generally relates to a driver assistance system for a vehicle, in particular a commercial vehicle, to a vehicle system with such a driver assistance system and to a method for controlling a brake system.

Driver assistance systems generally serve to assist the driver in controlling the vehicle during driving. Such systems can be, in particular, surroundings detection systems that detect foreign objects by means of suitable sensors, in order to change the driving behavior of the vehicle correspondingly. In this context, on the one hand, a collision with a detected external object can be prevented or the severity of an accident can be reduced by braking the vehicle suitably. Furthermore, a vehicle that is traveling ahead can be detected and the distance from the driver's own vehicle can be regulated, for example in the form of an ACC (adaptive cruise control) process or else as the vehicle traveling in a convoy mode in a line composed of a plurality of vehicles. In particular, radar-based or ultrasound-based sensors can be used as surroundings detection sensors for detecting distance, and video systems can be used for recording and detecting the objects and, if appropriate, for detecting distance through the evaluation of stereo images. Furthermore, the driver assistance systems may also be systems that detect a critical driving state, for example a tendency of the vehicle to tip over or a tendency of the vehicle to skid, and communicate this to the brake control device.

Driver assistance systems as systems that are implemented separately from the brake control device can output what are referred to as external brake request signals to the brake control device of the brake system, in particular via a data bus. The brake control device therefore carries out a control process of the brakes on the basis of internal brake signals, which may comprise, in particular, the setpoint brake request input by the driver via a brake value signal generator and, for example, internal closed-loop control processes such as ABS or else a stability control process, and on the basis of additional external brake request signals.

DE 101 18 708 A1 and DE 101 18 707 A1 describe processes for regulating vehicle speed and for preventing collisions, in which, when a possible imminent braking intervention is detected, a hydraulic brake system can be biased by already increasing the brake pressure of the brake hydraulics without an appreciable braking operation already being initiated. For this purpose, an appropriate flag can be set by a decision unit that also receives a brake request signal S1 of the driver. The actual braking operation can therefore subsequently be carried out more quickly since the corresponding pressure build-up of the brake hydraulics does not have to be initiated first so that time can be gained during the actual braking operation.

Such biasing when a relatively high probability of a collision is detected may be carried out in a hydraulic brake system in a directly internal fashion by means of the control device. However, in the case of pneumatic brake systems of commercial vehicles, surroundings detection systems are generally embodied as external systems that communicate with the brake control device, for example via a vehicle-internal data bus such as the CAN bus, and by means of suitable protocols. The external request for biasing without a braking effect, or without a relevant braking effect, would therefore require a suitable set of instructions that cannot be implemented with current systems.

In pneumatic brake systems of a commercial vehicle field, external brake requests can be requested by means of various standards. SAE-31939 describes the logging of such external brake requests, and, accordingly, an external brake request contains information about the priority, the control mode and the acceleration setpoint value.

The indication of the priority is relevant since, according to this standard, the external brake request signal is continuously output by the external system, with the result that when an actually necessary braking effect is absent a low priority is specified; in the case of a priority signal with three stages, the lowest priority can therefore be indicated. The control mode can, in particular, be additive or maximal; in the case of an additive control mode the external brake request is set in addition (additively) to the internally set braking effect, and, on the other hand in the case of a maximum control mode, formation of a maximum value is brought about, i.e., the highest value of the internal brake request and the highest value of the external brake request are respectively formed. Furthermore, the external brake request signal has an indication about the setpoint acceleration to be set or the acceleration setpoint value, wherein braking operations correspondingly have a negative value.

It is an object of the present invention to provide a driver assistance system for a vehicle, a vehicle system with such a driver assistance system and a corresponding method for controlling a brake system, which permit rapid initiation of a braking process in critical situations with relatively low expenditure.

This object is achieved by means of a driver assistance system as claimed in claim 1, a vehicle system as claimed in claim 11 and a method as claimed in claim 13. The dependent claims describe preferred developments.

According to an embodiment of the present invention, biasing of the brake system is already made possible when a sufficient probability of a critical state has been detected by an external driver assistance system in order to be able to initiate more quickly a possibly necessary braking operation at a later time. Depending on the driver assistance system, different critical states can be detected. In the case of a surroundings detection system, in particular a probability of a collision can be detected. In the case of an external driving stability system, instabilities of the vehicle itself or else unstable states of other vehicles of a vehicle-trailer combination can be detected and an external brake request signal can be formed therefrom and fed to the brake control device.

The invention permits, in particular, use in commercial vehicles in which in general pneumatic brakes are used in which relatively high values of mass inertia and relatively high lag times for overcoming the clearance and filling the wheel brake cylinders with the brake medium are present, for example 200 to 300 ms in the case of an EBS and 500 to 700 ms in the case of an ABS, compared to, for example, values of 100 to 150 ms in the case of a hydraulic brake system.

An external driver assistance system is understood according to the embodiments of the present invention to be a driver assistance system that is not configured as part of the brake control system and therefore outputs a brake request as an external brake request signal to the brake control device. This may occur, in particular, via a data bus of the vehicle, in particular the CAN bus. Biasing of the brake system is understood to mean increasing the pressure in the braking medium in order to overcome idle travel or clearance, with the result that braking surfaces are already entirely or largely in contact with one another, wherein, under certain circumstances, a small amount of wear already occurs on the braking surfaces with an, under certain circumstances, negligible braking effect.

It is another object of the present invention to permit biasing of the brake system by means of an external brake request signal, which is basically generally already present in such vehicles and is also used to initiate an actual braking process. In this context, this external brake request signal is set according to the invention in such a way that a high acceleration setpoint value is specified, which value will not bring about the initiation of an actual braking process when the signal is received by the brake control device. In this context it is, in particular, possible to predefine an acceleration setpoint value which is above the current actual acceleration value, i.e. is directed at a relatively high acceleration, while taking into account signs and absolute value, and therefore cannot be achieved by a braking operation, with the result that the brake system cannot set this value by activating brakes. Nevertheless, a high priority is advantageously set so that the signal has to be complied with.

The biasing of the brake system is therefore made possible by systems that are basically already present and existing protocols. The brake control device can receive the external brake request signal and interpret it such that at that particular time no actual braking operation is initiated, but owing to the high priority a biasing process in order to overcome the lag time is already initiated. In this context, the output of such an external brake request signal is not critical with respect to the safety of the vehicle since no actual braking operation is initiated yet and at most an insignificant deceleration is brought about due to the brake linings coming slightly into contact with the brake disk.

As a result, according to embodiments of the invention, biasing of the brake system can be initiated in a simple way by an external system using given protocol features.

The invention can be used, for example, in an emergency braking system such as AEBS, a collision mitigating system such as CMS, a collision warning system such as CWS, an adaptive cruise control system such as ACC or a convoy system for a plurality of vehicles, as well as in a predictive braking assistance system, a low speed collision warning system, in particular for turning maneuvers, for the purpose of protecting pedestrians, cyclists and other relatively vulnerable road users such as BSD, and in a driving stability system, for example for detecting tendencies to roll over, for example as an RSC (Roll Stability Control).

The invention will be explained in more detail below using a number of exemplary embodiments and with reference to the appended drawings, in which:

FIG. 1 shows a commercial vehicle having a driver assistance system according to an embodiment of the invention;

FIG. 2 shows an external brake request signal in accordance with an embodiment of the invention; and

FIG. 3 is a flowchart of a method for controlling a brake system according to an embodiment of the invention.

A vehicle 1 travels on a roadway 2 in the direction of travel F. The vehicle 1 is, here, a commercial vehicle with three axles and therefore six wheels 3-1, 3-2, 3-3, 3-4, 3-5 and 3-6. The vehicle brake system 4 has pneumatic brakes 4-1, 4-2, 4-3, 4-4, 4-5, 4-6 that each act on the wheels 3-1 to 3-6, with the result that the vehicle 1 can, for example, be braked on a wheel basis or axle basis. In this context, for example, a common compressed air accumulator (not shown) is provided for all the brakes 4-1 to 4-6, or else in a two-channel brake system two such compressed air accumulators are correspondingly provided for supplying compressed air to the pneumatic brakes 4-1 to 4-6. The brake system 4 also has a brake control device 6 that can be embodied, in particular, as a control unit known per se. The brake control device 6 can, however, also be formed by a plurality of units. The brake control device 6 receives brake request signals Si from a brake value signal generator 7 that can be actuated, in particular, by the driver in a manner known per se by means of the brake pedal. The vehicle 1 travels with a longitudinal acceleration a-ist that is positive in the example shown in FIG. 1.

Furthermore, a driving stability control, which detects a driving state of the vehicle 1 from sensor signals and can request, as a function thereof, stability interventions that lead to activation of the individual brakes 4-1 to 4-6, can be implemented in the brake control device 6. This may be, for example, an ABS controller and in addition, for example, also a relatively complex driving stability control for avoiding unstable states such as skidding, tilting etc., for which purpose, for example, the yaw rate and the lateral acceleration can be measured. These brake requests constitute internal brake requests of the brake system 4.

The vehicle 1 furthermore has a driver assistance system 14 that has a surroundings detection system 17 and a control unit 16. The surroundings detection system 17 has, in turn, one or more surroundings sensors 15-1, 15-2 and 15-3, and, if appropriate, further elements. The control unit 16 can, however, also be part of one of the sensors 15-1, 15-2 and 15-3. The sensors 15-1 to 15-3 are, for example, configured on a radar basis, laser basis, video image basis or ultrasound basis and detect foreign objects 20 in a surrounding area 19 on or next to the roadway 2. In this context, for example, a distance d of the vehicle 1 from the object 20 is detected. The driver assistance system 14 may be, for example, an ACC (Adaptive Cruise Control) system for setting a predefined distance d from a vehicle 20 that is traveling ahead, or else a system for bringing about automatic driving in a line with a plurality of further vehicles 20. Furthermore, the driver assistance system 14 can also be a collision warning system or a system for avoiding collisions or reducing possible collision damage.

The sensors 15-1 to 15-3 transmit measurement signals S5-1, S5-2, S5-3 to the control unit 16, which determines a brake request on the basis of these signals S5-1 to S5-3 and, if appropriate, stored data, and which outputs an external brake request signal S6 to the brake control device 6, for example via a vehicle-internal data bus such as the CAN bus 5. The external brake request signal S6 can optionally request braking of individual wheels or of all the wheels 3-1 to 3-6. The braking operation requested as a result of this is therefore initiated by the brake control device 6 in accordance with the content of the external brake request signal S6 after the external brake request signal S6 has been received. The brake request signal S6 may be, for example, an XBR message (external brake request) in accordance with the standard SAE J1939-71.

FIG. 2 shows an external brake request signal S6 in schematic form: the signal S6 accordingly contains a priority signal S6-1 for indicating the priority with which this entire brake request signal S6 is to be treated. In this context, the priority signal S6-1 may assume, for example, three levels, specifically lowest, medium and highest. Furthermore, the external brake request signal S6 has a control mode signal S6-2 that can assume, for example, the value “additive” or “maximum”; in the case of the “additive” mode, the external brake request is superposed additively on the brake request generated internally in the brake system 4, with the result that the external brake request is applied additionally or additively. In the case of the “maximum” mode, it is, on the other hand, only possible for the maximum value of the setpoint brake value that has already been requested internally by the brake system 4 and of the external setpoint brake value to be formed by the brake control device 6; the externally requested setpoint braking effect is therefore set only if it is higher than the internal brake request. The external brake request signal S6 also has an acceleration request signal S6-3 in which the requested setpoint acceleration value a-soll is given, for example with a negative sign when braking is requested and with a positive sign when an acceleration of the vehicle 1 is requested. Furthermore, the brake request signal S6 can also have further components.

The driver assistance system 14 determines, for example, a collision probability from the sensor signals S5-1 to S5-3 and outputs the external brake request signal S6 as a function of the determined collision probability. When a sufficiently high collision probability is detected, a change in the brake system 4 is already aimed at with the effect that the brakes 4-1 to 4-6 are biased. Biasing of the pneumatic brakes 4-1 to 4-6 means that the clearance thereof is overcome and therefore, if appropriate, slight contact between the brake linings and the brake disks may already occur. However, no appreciable braking is initiated in the event of such biasing of the brakes 4-1 to 4-6.

If the control unit 16 of the driver assistance system 14 wishes to bring about such biasing of the brake system 4 in order to prepare for—possible—later braking, it sets the priority signal S6-1 to the highest (or to a high) value, the control mode signal S6-2 to formation of a maximum value “maximum” and the acceleration setpoint value signal S6-3 or its acceleration setpoint value a-soll to such a high value that when the value is achieved no braking is initiated. This high value can therefore be, in particular, positive, i.e., a forward acceleration. This is shown, for example, in FIG. 1 by the arrow for a-soll, which is larger than the arrow for a-ist. The acceleration setpoint value signal S6-3 is therefore set, in particular, to an unrealistically high value, which can advantageously not be set at all by the braking operation; in particular, an acceleration setpoint value a-sol; can be requested that is larger than the current actual acceleration a-ist, i.e., a relatively strong, forwardly directed acceleration, which therefore cannot be set by a braking effect in any case since it would require a drive force instead of a braking force.

According to the inventive embodiments, the brake control device 6 interprets the external brake request signal S6 to the effect that, where there is a high priority, formation of maximum values and an external setpoint value of the acceleration that is so high that it cannot be achieved by a braking effect, a biasing process is initiated and the clearance of the brakes 4-1 to 4-6 is overcome. This is correspondingly confirmed in a corresponding response signal S7 from the brake control device 6 to the external control unit 16.

The embodiment of the method according to the invention shown in FIG. 3 therefore starts in step St0, for example already when the ignition of the vehicle 1 is switched on. The driver assistance system 14 according to step S0 subsequently continuously carries out detection of the surroundings, with the result that its control unit 16 correspondingly receives measurement signals 55-1 to S5-3 from its sensors 15 and evaluates them. If a direct need for braking is detected in the decision step St2, according to branch y an external brake request signal S6 is output with an actual brake request, i.e., with a high priority signal and an acceleration setpoint value signal S6-3 that is correspondingly negative in terms of its sign and correspondingly high in terms of its absolute value, with the result that the brake control device 6 carries out an immediate braking operation in step St3. If no immediate braking is detected in step St2, according to branch n in step St4 it is checked whether there is a sufficiently high probability of a collision, with the result that biasing of the brake system 4 is aimed at. If this sufficiently high collision probability is present, according to branch y the external brake request signal S6 is output with a high priority, maximum value mode and sufficiently high acceleration setpoint value signal 56-3, with the result that the brake control device 6 detects that no actual braking is desired but biasing of the brake system 4 is to be already initiated, and in step St5 this biasing is initiated.

If appropriate, further steps and additional braking interventions can be carried out according to FIG. 3; this flowchart shows only the steps that are most relevant to the invention. The method is in turn reset to before step St1 by all the steps St3 and St5. 

1. A driver assistance system (14) for a vehicle (1), in particular commercial vehicle, wherein the driver assistance system (14) has: a detection system (17) which has at least one sensor (15-1, 15-2, 15-3) for outputting measurement signals (S5-1, S5-2, S5-3), a control unit (16) for receiving the measurement signals (S5-1, S5-2, S5-3) and determining a probability of a critical situation or of a critical state of the vehicle (1), wherein, when a critical state or a sufficient probability of a critical state is detected, the control unit (16) of the driver assistance system (14) outputs a signal (S6) for biasing a brake system (4) to a brake control device (6) of the brake system (4) of the vehicle (1), and wherein the control unit (16) outputs an external brake request signal (S6) for initiating braking processes to the brake control device (6) of the brake system (4), characterized in that the control unit (16) outputs, for the purpose of biasing the brake system (4), an external brake request signal (S6) which has an acceleration setpoint value signal (S6-3) with a higher acceleration setpoint value (a-soli) than a current acceleration actual value (a-ist).
 2. The driver assistance system (14) as claimed in claim 1, characterized in that it is embodied outside the brake system (4) and outputs the external brake request signals (S6) to the brake control device (6) via a data line (5), in particular a data bus (5) of the vehicle.
 3. The driver assistance system (14) as claimed in claim 1 or 2, characterized in that the external brake request signal (S6) contains a priority signal (S6-1) which has a high priority for the purpose of setting the biasing of the brake system (4).
 4. The driver assistance system (14) as claimed in one of the preceding claims, characterized in that the external brake request signal (S6) has a control mode signal (S6-2) which, for the purpose of setting the biasing of the brake system (4), indicates formation of a maximum value between the external brake request value (a-soll) and an internal brake request value.
 5. The driver assistance system (14) as claimed in one of the preceding claims, characterized in that the detection system (17) is or has a surroundings detection system (17), and the at least one sensor (15-1, 15-2, 15-3) senses foreign objects (20).
 6. The driver assistance system (14) as claimed in claim 5, characterized in that the at least one sensor (15-1, 15-2, 15-3) determines distances (d) from the sensed external objects (20), and the driver assistance system (14) is provided for collision detection, collision reduction, an inter-vehicle distance maintaining system, a pedestrian detection system and/or a system for driving in a line automatically, wherein the control unit (16) checks for a collision with the detected external object (20) as the critical state of the vehicle (1), and when a sufficiently high probability of a collision is determined said control unit (16) outputs the external brake request signal (S6) for biasing the brake system (4).
 7. The driver assistance system (14) as claimed in one of the preceding claims, characterized in that the control unit (16) of the driver assistance system (14) detects an unstable driving state of the vehicle (1), for example an imminent rollover and/or skidding state of the vehicle (1), as a critical state, and when a sufficiently high probability of an unstable driving state of the vehicle (1) is determined said control unit (16) outputs the external brake request signal (S6) for biasing the brake system (4).
 8. The driver assistance system (14) as claimed in one of the preceding claims, characterized in that the acceleration setpoint value signal (S6-3) for biasing the brake system (4) has a positive acceleration setpoint value (a-soll) for a positive acceleration of the vehicle (1).
 9. The driver assistance system (14) as claimed in one of the preceding claims, characterized in that the external brake request signal (S6) is continuously output via a data bus (5) of the vehicle (1).
 10. The driver assistance system (14) as claimed in one of the preceding claims, characterized in that the control unit (16) is integrated into at least one of the sensors (15-1, 15-2, 15-3).
 11. A system for a vehicle (1) which has: a brake system (4) having a brake control device (6) and brakes (4-1, 4-2, 4-3, 4-4, 4-5, 4-6) for braking wheels (3-1, 3-2, 3-3, 3-4, 3-5, 3-6) of the vehicle (1), and a driver assistance system as claimed in one of the preceding claims, wherein the control unit (16) of the driver assistance system (14) outputs the external brake request signal (S6) to the brake control device (6) of the brake system (4), and the brake control device (6) initiates braking operations on the basis of an internal brake request and of the external brake request signal (S6) by applying a braking medium to the brakes (4-1 to 4-6), wherein the brake control device (6) initiates, for the purpose of biasing the brake system (4), an increase in the pressure of the braking medium in order to reduce a lag time in the event of a subsequent braking process.
 12. The vehicle system as claimed in claim 11, characterized in that the brake system (4) is a pneumatic brake system (4) having pneumatic brakes (4-1, 4-2, 4-3, 4-4, 4-5, 4-6), wherein the brake control device (6) overcomes clearance in the pneumatic brakes (4-1, 4-2, 4-3, 4-4, 4-5, 4-6) in order to bias the brake system (4).
 13. A method for controlling a brake system (4) of a vehicle (1) having at least the following steps: Detection of critical situations and/or critical states of the vehicle (1), in particular of collisions or instabilities of the vehicle, by a driver assistance system (14) (St1) and outputting of an external brake request signal (S6) from the external driver assistance system (14) to a brake control device (6) of the brake system (4) (St2, St4), wherein the brake control device (6) initiates braking operations of the vehicle (1) on the basis of internal brake requests and of the external brake request signal (S6), wherein the driver assistance system (14) requests biasing of the brake system (4) when a sufficient probability of a critical state and/or a critical situation is detected, characterized in that the driver assistance system (14) requests, for the purpose of biasing the brake system (4), an acceleration setpoint value (a-soll) which is higher than the current acceleration actual value (a-ist). 